This rare inborn error of metabolism, caused by a deficiency of 3-methyl crotonyl (3-MC) CoA carboxylase, leads to an accumulation of 3-MC CoA. Glycine therapy has been successfully used in other organic acidemias with success. Since the Km of the enzyme for glycine is higher than the extracellular glycine concentration, addition of glycine should increase flow through the pathway with excretion of 3-MC & lower plasma levels of the offending acid.